Learning and Memory during General Anesthesia: An Update

Abstract

(Ghoneim) Professor.(Block) Associate Professor.Received from the Department of Anesthesia, College of Medicine, University of Iowa, Iowa City, Iowa. Submitted for publication November 20, 1996. Accepted for publication March 27, 1997.Address reprint requests to Dr. Ghoneim: Department of Anesthesia, College of Medicine, University of Iowa, Iowa City, Iowa 52242.Dennis M. Fisher, M.D., EditorIn 1992, we published a review article in Anesthesiology on learning and consciousness during general anesthesia. [1] Since then, there has been a steady flow of publications and two international conferences on the subject; one in 1992 in Atlanta, Georgia, and another in 1995 in Rotterdam, the Netherlands. In 1992, the issue of preservation of unconscious information-processing capability by the anesthetized patient was debated because of the mixed results of studies at that time. We and others [2,3] thought that with improvement in the quality of work in this area, the issue of whether unconscious retention of intraoperative events is a reliable, replicable phenomenon might be resolved in a few years. Unfortunately, this has not happened. With conflicting reports and contradictory statements being published, we chose to update the reader on this and related subjects with particular emphasis on problems and difficulties in this area, and to provide some comments that we hope will be useful for future studies.Here we address the following issues.1. Explicit or conscious memory or “awareness”;2. Studies of anesthetized patients using implicit tests of memory;3. Postoperative motor behavior after presentation of suggestions during anesthesia;4. Studies of the efficacy of administration of therapeutic suggestions during anesthesia;5. Studies of healthy volunteers;6. Effects of anesthetics on animal learning and memory; and7. Reports of cases of psychosomatic disorders after anesthesia and surgery.In each area, we discuss in particular the studies that have been published since 1992, within the context of the earlier literature, followed by comments and critiques. We use the term consciousness as defining a state of awareness of the outside world and use the terms consciousness, awareness, and wakefulness interchangeably.Distinctions between different types of learning and memory remain the subject of considerable debate. One such distinction, of particular interest to anesthesia, is between explicit and implicit learning. The essential difference is whether learning is manifested with or without concurrent awareness of remembering. [4,5]The most recent study in which a structured interview was used in a large series of patients indicated that the incidence in nonobstetric and noncardiac surgical cases is 0.2%. [6] The incidence is similar after total intravenous anesthesia. [7] It is higher, however, when light anesthesia is used. The incidence in cardiac surgery ranges from 1.14–1.5%, [8,9] with a balanced anesthetic technique consisting of benzodiazepines, low-dose fentanyl, and a volatile agent. A higher incidence has been reported for obstetric cases [10](0.4%) and major trauma cases [11](11–43%), and this incidence varies according to the dose of anesthetic administered. Jones [12] estimates that only about 0.01% of patients report suffering from pain while being aware.Recently Cobcroft and Forsdick [13] and Moerman et al. [14] studied the consequences of recall of intraoperative events during anesthesia. Cobcroft and Forsdick described patients who responded to an article published by Forsdick about her own experience of awareness during anesthesia in a lay magazine widely distributed in Australia and New Zealand. Moerman et al. studied patients who were referred to them by anesthesiologists. Despite the different strategies of patient selection of the two groups, there was close agreement between the results. The two most frequent complaints were ability to hear events during surgery and sensations of weakness or paralysis, in addition to the recall of pain, if it was present. It seems that patients particularly recall conversations or remarks that are of a negative nature concerning themselves or their medical conditions. The most frequently reported postoperative effects were sleep disturbances, dreams and nightmares, flashbacks, and daytime anxiety.For many patients, the experience of awareness may not leave prolonged after effects; however, some develop post-traumatic stress disorder, marked by repetitive nightmares (usually poorly disguised replays of an operative situation), anxiety and irritability, a preoccupation with death, and a concern with sanity, that make the patients reluctant to discuss their symptoms. [15] It is not readily apparent why some patients develop a post-traumatic stress disorder and others do not.The medicolegal consequences of awareness remain of interest. Domino* recently analyzed claims from the American Society of Anesthesiologists Closed Claims Project. Claims for awareness during